Browsing by Author "Chen, Junqin"
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Item Open Access Dissimilar cavitation dynamics and damage patterns produced by parallel fiber alignment to the stone surface in holmium:yttrium aluminum garnet laser lithotripsy.(Physics of fluids (Woodbury, N.Y. : 1994), 2023-03) Xiang, Gaoming; Li, Daiwei; Chen, Junqin; Mishra, Arpit; Sankin, Georgy; Zhao, Xuning; Tang, Yuqi; Wang, Kevin; Yao, Junjie; Zhong, PeiRecent studies indicate that cavitation may play a vital role in laser lithotripsy. However, the underlying bubble dynamics and associated damage mechanisms are largely unknown. In this study, we use ultra-high-speed shadowgraph imaging, hydrophone measurements, three-dimensional passive cavitation mapping (3D-PCM), and phantom test to investigate the transient dynamics of vapor bubbles induced by a holmium:yttrium aluminum garnet laser and their correlation with solid damage. We vary the standoff distance (SD) between the fiber tip and solid boundary under parallel fiber alignment and observe several distinctive features in bubble dynamics. First, long pulsed laser irradiation and solid boundary interaction create an elongated "pear-shaped" bubble that collapses asymmetrically and forms multiple jets in sequence. Second, unlike nanosecond laser-induced cavitation bubbles, jet impact on solid boundary generates negligible pressure transients and causes no direct damage. A non-circular toroidal bubble forms, particularly following the primary and secondary bubble collapses at SD = 1.0 and 3.0 mm, respectively. We observe three intensified bubble collapses with strong shock wave emissions: the intensified bubble collapse by shock wave, the ensuing reflected shock wave from the solid boundary, and self-intensified collapse of an inverted "triangle-shaped" or "horseshoe-shaped" bubble. Third, high-speed shadowgraph imaging and 3D-PCM confirm that the shock origins from the distinctive bubble collapse form either two discrete spots or a "smiling-face" shape. The spatial collapse pattern is consistent with the similar BegoStone surface damage, suggesting that the shockwave emissions during the intensified asymmetric collapse of the pear-shaped bubble are decisive for the solid damage.Item Open Access Exploring optimal settings for safe and effective thulium fibre laser lithotripsy in a kidney model.(BJU international, 2024-02) Mishra, Arpit; Medairos, Robert; Chen, Junqin; Soto-Palou, Francois; Wu, Yuan; Antonelli, Jodi; Preminger, Glenn M; Lipkin, Michael E; Zhong, PeiObjectives
To explore the optimal laser settings and treatment strategies for thulium fibre laser (TFL) lithotripsy, namely, those with the highest treatment efficiency, lowest thermal injury risk, and shortest procedure time.Materials and methods
An in vitro kidney model was used to assess the efficacy of TFL lithotripsy in the upper calyx. Stone ablation experiments were performed on BegoStone phantoms at different combinations of pulse energy (EP ) and frequency (F) to determine the optimal settings. Temperature changes and thermal injury risks were monitored using embedded thermocouples. Experiments were also performed on calcium oxalate monohydrate (COM) stones to validate the optimal settings.Results
High EP /low F settings demonstrated superior treatment efficiency compared to low EP /high F settings using the same power. Specifically, 0.8 J/12 Hz was the optimal setting, resulting in a twofold increase in treatment efficiency, a 39% reduction in energy expenditure per unit of ablated stone mass, a 35% reduction in residual fragments, and a 36% reduction in total procedure time compared to the 0.2 J/50 Hz setting for COM stones. Thermal injury risk assessment indicated that 10 W power settings with high EP /low F combinations remained below the threshold for tissue injury, while higher power settings (>10 W) consistently exceeded the safety threshold.Conclusions
Our findings suggest that high EP /low F settings, such as 0.8 J/12 Hz, are optimal for TFL lithotripsy in the treatment of COM stones. These settings demonstrated significantly improved treatment efficiency with reduced residual fragments compared to conventional settings while keeping the thermal dose below the injury threshold. This study highlights the importance of using the high EP /low F combination with low power settings, which maximizes treatment efficiency and minimizes potential thermal injury. Further studies are warranted to determine the optimal settings for TFL for treating kidney stones with different compositions.Item Open Access In vitro investigation of stone ablation efficiency, char formation, spark generation, and damage mechanism produced by thulium fiber laser.(Urolithiasis, 2023-11) Chen, Junqin; Mishra, Arpit; Medairos, Robert; Antonelli, Jodi; Preminger, Glenn M; Lipkin, Michael E; Zhong, PeiTo investigate stone ablation characteristics of thulium fiber laser (TFL), BegoStone phantoms were spot-treated in water at various fiber tip-to-stone standoff distances (SDs, 0.5 ~ 2 mm) over a broad range of pulse energy (Ep, 0.2 ~ 2 J), frequency (F, 5 ~ 150 Hz), and power (P, 10 ~ 30 W) settings. In general, the ablation speed (mm3/s) in BegoStone decreased with SD and increased with Ep, reaching a peak around 0.8 ~ 1.0 J. Additional experiments with calcium phosphate (CaP), uric acid (UA), and calcium oxalate monohydrate (COM) stones were conducted under two distinctly different settings: 0.2 J/100 Hz and 0.8 J/12 Hz. The concomitant bubble dynamics, spark generation and pressure transients were analyzed. Higher ablation speeds were consistently produced at 0.8 J/12 Hz than at 0.2 J/100 Hz, with CaP stones most difficult yet COM and UA stones easier to ablate. Charring was mostly observed in CaP stones at 0.2 J/100 Hz, accompanied by strong spark-generation, explosive combustion, and diminished pressure transients, but not at 0.8 J/12 Hz. By treating stones in parallel fiber orientation and leveraging the proximity effect of a ureteroscope, the contribution of bubble collapse to stone ablation was found to be substantial (16% ~ 59%) at 0.8 J/12 Hz, but not at 0.2 J/100 Hz. Overall, TFL ablation efficiency is significantly better at high Ep/low F setting, attributable to increased cavitation damage with less char formation.Item Open Access The Effect of Surface Flaws on Nanosecond Shock Wave Induced Brittle Fracture(2020) Chen, JunqinNano pulse lithotripsy (NPL) is a novel medical technology to fragment urinary calculi through electrical discharge. Compared with traditional shock wave lithotripters utilizing focused shock waves, NPL is ideal for investigating the stress field induced by surface acoustic waves (SAWs), such as the leaky Raleigh waves (LRWs), on the fluid-solid boundary. A pioneering study has recently demonstrated the generation of LRWs induced by the spherically divergent shock wave at the borosilicate glass-water boundary in NPL treatment. The resultant tensile stress field was found to play an important role in the initiation of cracks and the formation of ring-like fracture on the glass surfaces. This prior work motivates us to investigate the effect of SAWs on surface flaws that can be artificially and controllably created on the glass surface by microindentations to mimic the surface erosion induced by cavitation. In this study, we used a microhardness tester with a Vickers indenter and applied a load of 1.0 kg with a dwell time of 10 s to produce indentations at various radial distances (1.0 mm, 1.5 mm, 2.0 mm and 2.5 mm) on the borosilicate glass samples (50 x 50 x 3.3 mm in LxWxH). Each indentation creates a pyramid shaped impression with an average diagonal length of 55 m and penetration depth of 7.8 m. At a standoff distance of 1.5 mm, the shock waves generated by the NPL probe were applied to the glass surface until the glass was broken. After each shock impact, the crack initiation and extension around each indentation site were recorded, from which the speed of crack development represented by the arc length per shock was calculated. Through these experiments, we have made the following important observations. First, the artificially induced surface flaws made by the microindentation can well control the location of the crack initiation since the presence of surface flaws will significantly weaken the glass surface. Under the effect of the maximum tensile stress (σ_(T,max)) generated by NPL shock wave impact, the cracks extending from the indentation impression site are predominantly aligned perpendicular to the direction of LRWs (which is also the direction of σ_(T,max)). Second, compared with the number of shocks required to initiate the ring-like fracture on the original (untreated) glass surface, fewer shock waves are needed to initiate the ring-like crack formation and extension from the impression site presumably due to the higher stress concentration built up at the tip of the surface flaws during NPL, which can greatly reduce the tensile stress or stress integral required to initiate a crack. The average speed of ring-like fracture formation at a radial distance about 1.5 mm is 0.26 mm per shock on the glass without microindentations. By contrast, the average speed of crack extension at the same radial distance with microindentations can increase to 0.34 mm per shock. Furthermore, the speed of crack extension varies with the radial distance of the microindentation from the NPL probe axis, largely following the variation of the local tensile stress integral generated by the LRWs. Altogether, these findings suggest potential synergy between shock wave-induced LRWs and surface flaws (e.g., produced by cavitation erosion pitting during shock wave lithotripsy) that may lead to improved stone comminution, which warrants future investigations.
Item Open Access Three-dimensional super-resolution passive cavitation mapping in laser lithotripsy(IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2024-01-01) Li, Daiwei; Wang, Nanchao; Li, Mucong; Mishra, Arpit; Tang, Yuqi; Vu, Tri; Xiang, Gaoming; Chen, Junqin; Lipkin, Michael; Zhong, Pei; Yao, JunjieKidney stone disease is a major public health issue. By breaking stones with repeated laser irradiation, laser lithotripsy (LL) has become the main treatment for kidney stone disease. Laser-induced cavitation is closely associated with the stone damage in LL. Monitoring the cavitation activities during LL is thus crucial to optimizing the stone damage and maximizing LL efficiency. In this study, we have developed three-dimensional super-resolution passive cavitation mapping (3D-SRPCM), in which the cavitation bubble positions can be localized with an accuracy of 40 μm, which is 1/10th of the acoustic diffraction limit. Moreover, the 3D-SRPCM reconstruction speed has been improved by 300 times by adopting a GPU-based sparse-matrix beamforming approach. Using 3D-SRPCM, we studied LL-induced cavitation activities on BegoStones, both in free space of water and confined space of a kidney phantom. The dose-dependence analysis provided by 3D-SRPCM revealed that accumulated impact pressure on the stone surface has the highest correlation with the stone damage. By providing high-resolution cavitation mapping during LL treatment, we expect that 3D-SRPCM may become a powerful tool to improve the clinical LL efficiency and patient outcome.